OK lets flip this thing over and vote for the best acted, or quintessential moment.
I HAVE to say its in GFII when Don Fennuccio pinches DeNiro's cheek after Vito deals with the "devil"... then the scene ligners and DeNiro touches his cheek and checks it for..... who knows what? ... is this the origen of the face wiping gesture we see in the older Vito? Wiping away that initial touch of evil?